SyntaxError: invalid syntax

[Danielgb23]

I get the following error trying to use make-deb on the source code from kitty, cloned from here.

 File "/home/USER/Downloads/kitty/setup.py", line 63
    action: str = 'build'
          ^
SyntaxError: invalid syntax

This is the part of the code from the kitty repo causing trouble:

class Options(argparse.Namespace):
    action: str = 'build'
    debug: bool = False
    verbose: int = 0
    sanitize: bool = False
    prefix: str = './linux-package'
    incremental: bool = True
    profile: bool = False
    libdir_name: str = 'lib'
    extra_logging: List[str] = []
    extra_include_dirs: List[str] = []
    link_time_optimization: bool = 'KITTY_NO_LTO' not in os.environ
    update_check_interval: float = 24.0
    shell_integration: str = 'enabled'
    egl_library: Optional[str] = os.getenv('KITTY_EGL_LIBRARY')
    startup_notification_library: Optional[str] = os.getenv('KITTY_STARTUP_NOTIFICATION_LIBRARY')
    canberra_library: Optional[str] = os.getenv('KITTY_CANBERRA_LIBRARY')